Subarna Dey

Covalent triazine-based frameworks (CTFs) from triptycene and fluorene motifs for CO2 adsorption

Two microporous covalent triazine-based frameworks (CTFs) with triptycene (TPC) and fluorene (FL) backbones have been synthesized through a mild AlCl3-catalyzed Friedel–Crafts reaction, with the highest surface area of up to 1668 m2 g−1 for non-ionothermal CTFs. CTF-TPC and CTF-FL show an excellent carbon dioxide uptake capacity of up to 4.24 mmol g−1 at 273 K and 1 bar.

A photoluminescent covalent triazine framework: CO2 adsorption, light-driven hydrogen evolution and sensing of nitroaromatics

A highly photoluminescent (PL) porous covalent triazine-based framework (PCTF-8) is synthesized from tetra(4-cyanophenyl)ethylene by using trifluoromethanesulfonic acid as the catalyst at room temperature. Due to triazine units in the framework, the PCTF-8 exhibits excellent thermal stability (>400 °C). The Brunauer–Emmett–Teller (BET) specific surface area of PCTF-8 is 625 m2 g−1 which is lower than the one obtained from the synthesis under Lewis acid conditions (ZnCl2). At 1 bar and 273 K, the PCTF-8 adsorbs a significant amount of CO2 (56 cm3 g−1) and CH4 (17 cm3 g−1) which is highly comparable to nanoporous 1,3,5-triazine frameworks (NOP-1-6, 29–56 cm3 g−1). This nitrogen rich framework exhibits good ideal selectivity (61 : 1 (85% N2 : 15% CO2) at 273 K, 1 bar). Thus, it can be used as a promising candidate for potential applications in post-combustion CO2 capture and sequestration technologies. In addition, photoluminescence properties as well as the sensing behaviour towards nitroaromatics have been demonstrated. The fluorescence emission intensity of PCTF-8 is quenched by ca. 71% in the presence of 2,4,6-trinitrophenol (TNP). From time-resolved studies, a static quenching behaviour was found. This high photoluminescence property is used for hydrogen evolving organic photocatalysis from water in the presence of a sacrificial electron donor and a cocatalyst.

Two linkers are better than one: enhancing CO2 capture and separation with porous covalent triazine-based frameworks from mixed nitrile linkers

Covalent triazine-based framework (CTF) materials were synthesized by combining two different nitrile building blocks: the tetranitrile tetrakis(4-cyanophenyl)ethylene (M) was reacted with either terephthalonitrile (M1), tetrafluoroterephthalonitrile (M2), 4,4′-biphenyldicarbonitrile (M3) or 1,3,5-benzenetricarbonitrile (M4) under ionothermal conditions (ZnCl2, 400 °C) to yield mixed-nitrile MM′-CTFs MM1 to MM4. Comparative 1H/13C and 19F/13C CP MAS analyses of MM2(300) (synthesized at 300 °C) suggest that the hydrogenated and fluorinated carbon atoms are in close vicinity (<5 A) to each other and support the formulation of the MM2(300) sample as a copolymeric CTF. Systematic N2, CO2 and CH4 gas sorption studies were performed up to 1 bar at 273 K and 293 K. The specific BET surface areas of MM1–MM4 were 1800, 1360, 1884 and 1407 m2 g−1, respectively. The CO2 uptake capacity of mixed-nitrile MM1, MM2 and MM4 was higher than the CO2 uptake of the respective individual single-nitrile M- or M′-CTF despite a higher surface area of the M-CTF PCTF-1 (2235 m2 g−1). The synergistic increase in the CO2 uptake of the mixed-nitrile MM′-CTFs is due to the higher CO2-accessible micropore volume Vmicro(CO2) and the higher micropore volume fraction V0.1/Vtot of the MM′-CTFs compared to the M- or M′-CTFs. The surface area of porous materials does not play the most important role in CO2 storage at low pressure but the CO2-accessible micropore volume is the more decisive factor. Further, MM2 shows the second highest (of known CTFs synthesized at 400 °C) CO2 uptake capacity of 4.70 mmol g−1 at 273 K and 1 bar because of its large micropore fraction (82%), which may be due to the release of fluorous decomposition products (‘defluorination carbonization’) during its synthesis. The CO2/N2 adsorption selectivities of mixed-nitrile MM1, MM2 and MM4 CTFs were also higher than those of the single-nitrile component M- or M′-CTFs.

Syntheses of two imidazolate-4-amide-5-imidate linker-based hexagonal metal–organic frameworks with flexible ethoxy substituent

A rare example of in situ linker generation with the formation of soft porous Zn- and Co-MOFs (IFP-9 and -10, respectively) is reported. The flexible ethoxy groups of IFP-9 and -10 protrude into the 1D hexagonal channels. The gas-sorption behavior of both materials for H2, CO2 and CH4 showed wide hysteretic isotherms, typical for MOFs having a flexible substituent which can give rise to a gate effect.

Synthesis of a partially fluorinated ZIF-8 analog for ethane/ethene separation

The separation of ethane/ethene mixtures (as well as other paraffin/olefin mixtures) is one of the most important but challenging processes in the petrochemical industry. In this work, we report the synthesis of ZIF-318, isostructural to ZIF-8 but built from the mixed linkers of 2-methylimidazole (L1) and 2-trifluoromethylimidazole (L2) (ZIF-318 = [(Zn(L1)(L2)]n). The synthesis has been optimized to proceed without ZnO-formation. Using only the L2 linker under solvothermal conditions afforded ZnO-embedded in the H-bonded and non-porous coordination polymer ZnO@[Zn2(L2)2(HCOO)(OH)]n. The slight differences in the size of the substituents (–CH3vs. –CF3) possibly in combination with different electronic inductive effects led to small but significant changes to the pore size and properties respectively, though the effective pore opening (aperture) size of ZIF-318 remained the same in comparison with ZIF-8. ZIF-318 is chemically (boiling water, methanol, benzene, and wide pH range at room temperature for 1 day), thermally (up to 310 °C) stable, and more hydrophobic than ZIF-8 which is proven by contact angle measurement. ZIF-318 can be activated for N2, CO2, CH4, H2, ethane, ethane, propane, and propene gases sorptions. Consequently, in breakthrough experiments, the ethane/ethene mixtures can be separated.